原式=5/7*(9/11-2/11)
=5/7*7/11
=5/11
简便计算
9/11÷(7/5)-2/11×5/7
=9/11x5/7-2/11×5/7
=（9/11-2/11）x5/7
=7/11x5/7
=5/11
9/11÷(7/5)-2/11×5/7
=9/11×5/7-2/11×5/7 ...........除法转化成乘法
=5/7×（9/11-2/11） ...........乘法的分配律
=5/7×7/11
=5/11
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